It's not an autoplaylist in my version (1882) and has not been in any of many previous versions I have used.

1) Autoplaylists have a differently coloured arrow and Recently Added Content has the same colour as ordinary playlists.

2) Right-clicking on it does not bring up the option Edit AutoPlaylist like other autoplaylists do. Instead there is an option to Edit Playlist, but like all ordinary playlists this just allows the user to edit the Name and View As...

You are correct. I was thinking of the default 'Recently Added' autoplaylist, but 'Recently Added Content' is a set of normal playlists created when you add files to your library.

That option creates a separate playlist for each import action and files added a minute apart would be in different playlists. Following that thought I think what you're requesting is for the group of playlists in the media tree to be sorted newest first, rather than sorting the contents of individual playlists.
E.g. playlist 'Added 2019-02-15 22:45' should appear higher in the list than 'Added 2018-01-04 21:00'.

I don't think this would be possible because the playlist tree is sorted alphabetically and not by date. It isn't even possible to drag the playlists to the order that you want.

I mean it could not be done with the current playlist tree and would require recoding the way the tree works.

They could easily add a single line of code to sort the playlists Z to A, but that would affect all of your playlists and not just the playlists which are children of 'Recently Added Content'.

The sort order itself is trivial, but to implement it would require an additional database field specifying the order that child-playlists should be sorted for each playlist.
Adding an extra database field then might also require an additional compatability check for databases that were saved with a version of MM prior to adding this feature.
It would also require adding an extra item to the playlist context menu and to the Edit menu allowing the user to specify the sort order.
Adding menu items then means adding an extra text string which then needs to be translated into the 31 languages available in MMW.

I would actually like to see the idea go a bit further and allow the user to drag playlists into the order they want, with an option to automatically sort alphabetically. Then I could have all my podcast playlists together and all my TV playlists together without requiring a parent-child relationship.